Makeup air heater



MAKEUP AIR HEATER Filed April 16. 1968 INVENTOR.

777e0dare J dyer/far? Arm/we y.

United States Patent 3,482,825 MAKEUP AIR HEATER Theodore J. Bjerkan, Prairie Village, Kans., assignor to Combustion Equipment Company, Kansas City, Mo.,

a corporation of Missouri Filed Apr. 16, 1968, Ser. No. 721,665 Int. Cl. F24h 3/04 U.S. Cl. 26319 Claims ABSTRACT OF THE DISCLOSURE A heater for air introduced into a point or factory to replace air exhausted therefrom by exhaust fans commonly employed, consisting of a large duct communicating with the outside atmosphere, a burner and blower in said duct for heating and delivering outside air to said plant, and an air turbulence inducer in said duct to insure delivery of air at a generally uniform temperature.

This invention relates to new and useful improvements in plant of factory ventilation, and has particular reference to that class of equipment commonly known as makeup air heaters. Many factories and plants employ exhaust fans, often a multiplicty thereof, to remove objectionable or noxious fumes and gases. Originally air leakage into the building through and around doors and windows was relied on to feed the exhaust fans to ventilate the plant. However, many modern plants are comparatively wellsealed, having relatively few and better fitting doors and windows, with the result that the exhaust fans tend to produce a partial vacuum in the plant. This partial vacuum results in higher exhaust fan power requirements, allows concentrations of undesirable gases to build up within the plant, hinders good air circulation, reduces the rate of air exchange in plant, and for these reasons generally reduces worker comfort and efliciency. For these reasons, it has become accepted practice to introduce air into the plant to makeup that removed by the exhaust fans. Generally, such makeup devices comprise large ducts extending into the plant from outdoors, having blowers therein for sucking air through the duct from outside, and discharging it into the plant. Generally, this solves all of the above enumerated problems, preventing the formation of partial vacuum and build-up of toxic gases in the plant, and improving circulation and rate of air exchange.

However, in cold weather this makeup air obviously must be heated, and this necessity has given rise to a distinct problem. The ducts employed are usually quite large, often being 90 inches square or even larger, it is not for various reasons practical to employ burners or heaters in the duct operable to heat the air uniformly over the entire cross-sectional area of the duct, and the fan-type blowers commonly employed have a pronounced tendency to produce a streamline or laminar flow of air through the duct with little turbulence. As a result, air heated in a restricted portion of the duct area tends to be discharged in the same portion of the outlet area. Thus, if the outlet is directly into the plant, some workers will receive cold air, and others hot air, and if the outlet is subdivided into smaller ducts for transmission to different plant areas, some of the smaller ducts will receive cold air and others hot air. The temperature gradient over the discharge area of the duct can be extreme. For example, with the structure I have shown, without the modifications forming the subject matter of my invention, the temperature gradient was often 200 degrees Fahrenheit or more, even in a duct 48 inches square.

Accordingly, the primary object of the present invention is the provision of means, in a makeup air heater of the character described, of means for producing a generally 3,482,825 Patented Dec. 9, 1969 "ice uniform temperature of the air discharged, over the entire discharge area. Generally, this object is accomplished by the provision of an air impeller so mountedin the duct as to break up the laminar or streamline air flow induced by the fan-type blower, whereby to produce sufficient turbulence to intermix the air thoroughly over the duct area prior to its discharge from the duct.

Another object is the provision of a makeup air heater of the character described wherein the turbulence producing air impeller is of such a type as to produce only a minimal and insignificant reduction in the efliciency or air-delivery capacity of the fan-type blower. For this purpose said impeller is of such construction as to produce only a radial impulse of the air, at right angles to the duct axis, and to have little or no direct effect on longitudinal flow.

Other objects are simplicity and economy of construction, efliciency and dependability of operation, and adaptability for use generally in air-flow ductsin which for any reason it may be desirable to introduce a degree of turbulence.

With these objects in view, as well as other objects which will appear in the course of the specification, reference will be had to the accompanying drawing, wherein:

FIG. 1 is a longitudinal, vertical mid-sectional view of a makeup air heater embodying the present invention, with parts left in elevation,

FIG. 2 is a sectional view taken on line 11-11 of FIG. 1, and

FIG. 3 is an enlarged sectional view taken on line IIIIII of FIG. 1, partially broken away.

Like reference numerals apply to similar parts throughout the several views, and the numeral 2 applies to the air duct forming the body of the makeup air heater comprising the subject matter of the present invention. As shown, said duct is of square cross-sectional contour, and is horizontally disposed, being provided with a channeliron base 4 by means of which the duct may be mounted, for example, on the roof of a factory or plant. Said duct is open at one end to the atmosphere, having an air inlet 6 hooded as at 8 to prevent the entry of rain or the like, and at its opposite end has a downwardly directed outlet 10 which may be interconnected to the interior of the plant through the roof thereof. The inlet opening 6 is controlled by a louvered damper 12, the louvers of which may be opened or closed by any suitable control means, said control means forming no part of the subject invention and hence not being shown. The size of the duct is often quite large, ducts inches square, or of 90 inches diameter, or even larger, not being unusual.

Adjacent the duct outlet, the duct is interrupted by :a partition wall 14 having a large central aperture 16 in which is concentrically mounted a vaned, fan-type blower 18. Said blower is carried by a shaft 20 disposed coaxially in duct 2 and rotatable in bearings 22 carried by a spider framework 2-4 aflixed to wall 14. Shaft 20 extends forwardly, or toward the inlet end of the duct, and has affixed thereon a pulley wheel 26 which is operably interconnected by drive belts 28 with a pulley 30 mounted on the output drive shaft 32 .pf an electric motor 34 mounted on base 4 at one side of duct 2. Pulley 26 and that portion of belts 28 within duct 2 are enclosed by a belt housing 36.

A gas-burning heater unit 38 is mounted in duct 2 adjacent the inlet end thereof, just inwardly of damper 12, said burner being mounted by any suitable means, and having the usual automatic controls, which form no part of the present invention and are not shown. As shown, the heater is of the bar or straight line type, discharging heat from a narrow, horizontally extending rectangular mouth facing in the direction of air travel,

and occupying only a small portion of the total crosssectional area of the duct.

The structure thus far described is already well-known. The modification thereof contemplated by the present invention consists of the addition of an air impeller wheel 40 to shaft 2.0 on a portion of said shaft extended from pulley 26 toward the inlet end of duct 2. As shown, said air impeller wheel consists of a hub 42 aflixed to said shaft, and a plurality of planar vanes 44 aflixed in and extending radially from said hub. For reasons which will presently be discussed, said vanes are disposed in planes parallel to shaft 20, and the impeller wheel is of a diameter no more than slightly greater than half the diameter of blower fan 18, and is spaced apart from said blower fan by a distance approximately equal to its diameter.

In the operation of the heater without. impeller wheel 40, blower fan 18 tends to create a laminar or streamline flow of air through duct 2, the mass of moving air moving through the duct being perhaps rotated somewhat about its axis by said fan, but with very little internal turbulence. Fans of this type have very little centrifugal or radially outward effect on the air, but provide forces tending to move the air primarily in a direction parallel to the fan axis. Thus, since heater 38 heats the air in only a limited fraction of the duct area, the heater air tends to remain in the same limited portion of the duct area throughout its length, even through fan 18, and as a result there often occurs a radical temperature gradient over the area of the discharge outlet 10 of the duct. As previously mentioned, tests have shown a variation of over 200 degrees Fahrenheit in the air discharged from different portions of outlet 10, even if the duct is as small as 48 inches square. The variation is still greater in larger ducts. Needless to say, this results in uneven, ineflicient heating of the plant area, and of course discomfort, sometimes extreme, to the workers in the plant.

Various attempts have been made to solve this problem. For example, ring burners or grid burners, operable to heat the air more evenly over the entire duct area, have been used in place of heater 38. However, all such more involved heaters have been subject to certain disadvantages, in that they are relatively costly, obstruct air flow and hence reduce the air capacity of the device or require greater power to drive the fan, and have a lower turn-down ratio. That is, the rate of fuel consumption, to accommodate the device for use in all outdoor temperature ranges, cannot be varied over as wide a range as in smaller burners r heaters. Bafiles have been employed in duct 2, or the duct itself made longer or more sinuous to provide the desired turbulence to intermix the air to a uniform temperature, but these means also severely reduced the air capacity of the device. A centrifugal blower, such as a squirrel-cage type, substituted for fan 18, would also be a partial solution to the problem, but is inherently relatively costly.

Air impeller wheel 40 appears to solve the problem to an effective degree in an extremely simple, economical manner. For example, tests have shown. that with said impeller wheel installed as shown, there is a temperature gradient over the duct discharge area of less than 30 degrees Fahrenheit, under the same conditions that produced a gradient of over 200 degrees before said impeller wheel was installed, and without significant reduction in the air transporting capacity of the duct. Said impeller wheel, since the planes of its vanes 44 are parallel to the duct axis, have very little direct eifect on air travel longitudinally of the duct, but does create radially outward drafts therefrom which tend to interrupt the streamline air flow generated by fan 18, to cause tubulence just sufiicient to intermix the air zones of different temperatures to a reasonably uniform overall. temperature.

Tests have also shown that the size and placement of impeller wheel 40 is of considerable importance. For example, the diameter of wheel 40 should be no more than slightly greater than one-half the diameter of fan 18. Good results have been obtained by making wheel 40 twenty-four inches in diameter when fan 18 is fortytwo inches in diameter. A greater diameter of wheel 40 tends to produce too great a degree of turbulence, with resultant loss of air capacity or a greater power requirement to turn the fan, while a lesser diameter of 'Wheel 40 will not produce the degree of turbulence required for air discharge at the desired uniformity of temperature. Also, wheel 40 should be spaced apart from fan 18 by a distance equal to or greater than the diameter of the former. If spaced more closely than this, the turbulence created by wheel 40 does not have suflicient time to mix the air to a uniform temperature before said air is again subjected to the streamlining elfect of fan 18, and some of the temperature evening effect would be lost. This would be true even if wheel 40 were disposed at the downstream side of fan 18, since the streamline or straight air flow is in either event strongest at and directly adjacent the fan. These proportions are not extremely critical, and are subject to variation, but are generally valid for best performance. They are also based somewhat on the fact that wheel 40, as shown, is mounted on the same shaft, and hence turns at the same speed, as fan 18. If wheel 40 were mounted and driven independently of fan 18, at any desired speed, then further variations in the size, configuration and position thereof would be possible, but the structure shown is far more economical and practical.

While I have described and claimed a specific embodiment of my invention, it will be readily apparent that many minor changes of structure and operation could be made without departing from the spirit of the invention as defined by the scope of the appended claims.

What I claim as new and desire to protect by Letters Patent is:

1. A makeup air heater comprising:

(a) an elongated duct adapted to interconnect the interior of a building with the oudoor atmosphere,

(b) a blower mounted in said duct and operable to draw outdoor air inwardly through said duct and to discharge it into the interior of said building, said blower being of the rotary fan type, coaxial with said duct, operable to produce a primarily streamline flow of air longitudinally through said duct with little internal turbulence,

(c) a heater unit disposed in said duct upstream from said blower and operable to heat air in a limited portion of the cross sectional area of said duct,

((1) an air impeller wheel disposed rotatably in said duct intermediate said blower and said heater and operable when driven to produce air currents in said duct transverse to the axis thereof, said air impeller wheel being disposed coaxially with said blower fan, being rotated at the same speed as said blower fan, and being of the radial vane type, the vanes thereof being planar with their planes parallel to the duct axis, whereby to apply forces to the air in the duct primarily only transversely to the duct axis, with very little direct effect on the longitudinal flow of air in said duct, and

(e) means for driving said impeller wheel.

2. A makeup air heater as recited in claim 1 wherein the diameter of said air impeller wheel is no more than slightly greater than one-half the diameter of said blower fan.

3. A makeup air heater as recited in claim 1 wherein said air impeller wheel is spaced apart from said blower fan, longitudinally of said duct, by a distance at least as great as the diameter of said impeller wheel.

4. A makeup air heater as recited in claim 1 wherein the diameter of said air impeller wheel is no more than slightly greater than one-half the diameter of said blower fan, and wherein said air impeller wheel is spaced apart from said blower fan, longitudinally of said duct, by a 5 distance at least as great as the diameter of said impeller wheel.

5. A makeup air heater as recited in claim 1 wherein said blower fan and said air impeller wheel are both fixed on a common rotatable shaft, whereby said means for driving said impeller wheel is also operable to drive said blower fan.

References Cited FOREIGN PATENTS 312,089 2/1956 Switzerland.

5 EDWARD G. FAVORS, Primary Examiner 

